Technical Abstract:
Avocado production in Israel and California, USA is facing a serious threat due to damage caused by an invasive Euwallacea ambrosia beetle and a novel Fusarium that it cultivates as a source of food. Adult female beetles possess mandibular mycangia within which they carry the Fusarium symbiont. At least nine fusaria, all of which appear to be farmed by Euwallacea spp., form a novel clade within the F. solani species complex based on phylogenetic analyses of multilocus DNA sequence data (Kasson et al. 2013). With the exception of F. ambrosium, the eight other species-level lineages were new to science. The Fusarium species cultivated by the Euwallacea sp. inhabiting avocado trees in Israel and California was characterized phylogenetically and morphologically. Molecular phylogenetic analyses of DNA sequences from portions of four genes (i.e., EF-1a, RPB1, RPB2 and ITS+LSU rDNA) indicated that it was an undescribed species closely related to F. ambrosium. Morphological comparison of the fungus in Israel/California, F. ambrosium and related species revealed that most of the Fusarium symbionts formed characteristic “dolphin-shaped” multiseptate conidia that were similar in size and swollen distally. In contrast to the other fusaria, the novel species in Israel/California formed dark green masses of sporodochial conidia after 1 month cultivation on potato dextrose agar. Microscopic examination of the dark green sporodochia revealed that many conidia possessed bluish and brownish pigmentation, while some were hyaline. None of the other fusaria including F. ambrosium produced the combination of remarkable dark green conidial masses and conidia with bluish or brownish pigmentation. Given the morphological and molecular phylogenetic findings, the symbiotic fungus in Israel/California was formally described as the novel species F. euwallaceae (Freeman et al. 2013).